Capping head for tamper-proof cap



Feb- 5 1963 H; R. LUEDI Erm. 3,076,300

CAPPING FOR TAMPER-PROOF CAP Filed Nov. 7. 1960 H uam CHlzlsTlAN H. STETTLER OSCAR Mij/My Md n!! im AT1-Ys 32 bij United Stats The `present invention relates to capping machines and more particularly to a machinefor applying caps of the trent tampereproof type to cans and other containers and which is particularly useful where the necks of the containers vmay be` cocked inV one direction or. another at a slight angle.

Y in a well-known type of tamper-proof cap the cap consists of two portions, an upper portion and a skirt portion,

off the bridges are ruptured freeing the` cap and offering positive proof that the vessel has been opened. Capping machines have been constructed in the past which are capable of applying torque to seat the cap and, thereafter,

spinning in the skirt of the cap about a suitable shoulder. Such devices have` given reasonably satisfactory results where the neck of the container is in perfect alinernent with the capping head. However it often happens, in the case of light gauge metal containers, particularly those using a soldered joint, that the head is not ELsquarely affixed but is cocked at a slight angle in one direction or the other. Efforts have been made to accommodate this cooking by providing a floating mount interposed between the chuck and the drive spindle of the capping device, but this produces an undesirable wobbling action which substantially limits the speed at which the device may be operated and which also makes it impossible to secure symmetrical spinning action, particularly Where the angle of vcooking is substantial.

It is, accordingly, the primary object of the present invention to provide a capping head which is capable of `producing uniform sealing of tamper-proof caps regardless of the cooking which may exist in the neck of the container being sealed. It is a related object to provide a capping head which is capable of yoperating at a high rate of speed without any vibratory wobbling action. It is a related object to provide a capping head which automatically accommodates itself to a Wide range of cooking angle and which is particularly well suited for use in a container-filling production line 4operated at a high rate of 3,076,301) Patented Feb. 5, id

rollers for spinning the skirt of the cap into locking posi- `tion progressively upon advancement of the drive spindle but in which the components which perform these functions are integrated into a compact cylindrical shape and minimum. diameter, thereby permitting the head to be ,used closely adjacent obstructions such as carrying handles which, are secured to the tops of containers, especially those having a capacity of two gallons or less.

Finally it is an object of the invention to provide a capping `head. for applying tamper-proof caps which is simple and inexpensiveto manufacture and which is capable of performing through many thousands of cycles consistently and Without any care or maintenance.

Other objects and advantages of the invention will become apparent upon reading the attached description and upon reference to the drawing in which:

FIGURE 1 is a vertical section taken through a capping head constructed in accordance with the present invention.

FIG. 1a is the top `view of a cap usable with the cap-V ping head. FIG. 2 is a transverse section taken along the line 2 2 in FIG. 1.

FIG. 3 is a vertical section similar to FIG. l but showing the head in rocked position accommodating itself to the cocked neck of a container encountered in a filling `and capping production line.

FIG. 4 is a fragmentary, enlarged section showing a i 4spinning roller acting upon the skirt portion of a typical it is another object to provide a capping head capable of performing the functions of tightening and spinning, with the two functions being coordinated in a novel fashion to insure that the cap is firmly seated in its final sealing position before the skirt of the cap is spun into place. In this connection it is an object of the invention to provide novel, long-wearing chuck mechanism to twist the cap into seated position with a precise and adjustable vamount of torque.

It .is a further object of the invention to provide a novel capping head'whioh is capable of rocking into alinerestored into alinement with the spindle axis automatically cap. t

While the invention has been described in connection with a preferred embodiment, it will be understood that invention is not limited to the particular embodiment shown, but is equally applicable to other modifications and alternative constructions included within the spirit and scope of the appended claims.

-Referring now tothe drawing there is shown in FIG. 1 a capping head 1t) having a drive spindle 11 and a mount 12 on the lower end thereof. Secured to the mount is a frame. 15 having a chuck 20 at its lower end.` Seated within the chuck is a friction disc 21 of rubber or the like. Surrounding the chuck 2t) is a spinning mechanism 25 which includes a plurality of spaced spinning members 26, 27, 28 respectively.

In use the capping head 10 is mounted in a standard machine chuck having provision for axial advancement as well as power rotation, analogous to a drill press, and the rotating head is fed down into engagement with a threaded cap or closure which is centered below it. A

typical cap, indicated at 30 in FlGS. la, 3 and 4, has an upper or threaded portion 31, and a lower or skirt portion 32 with the two portions being formed integral with one another and interconnected by narrow bridges 33 dening elongated slots 34. A cap of this kind is adapted to be screwed onto a threaded neck 35 of a container 36, of which onlyra portion is shown in FIG. 3. Arranged on the neck slightly below the level of the thread is an annular ridge or shoulder 37. It is the purpose of the spinning means 25 to engage the skirt portion 32 of the cap, spinning the same inwardly `so that it embraces and conforms to the lower surface of the shoulder 37. This serves to hold the cap in captive position. The bridges 33 are purposely designed for easy rupture, so -that when the cap is untwisted by manual effort the bridges break with the lower portion of the cap remaining permanently in place and providing positive visual indication in that the conrainer has been opened. In carrying out the present invention the three spinning members 26, 27, 28 are in the form of rollers mounted for radial -movement inwardly against the skirt portion of the cap upon continued downward advancement of the spindle 11.

In accordance with one of the aspects of the present invention, the frame is formed of two relatively telescoping portions having springs to maintain the two portions in extended position, with means for utilizing the relative telescoping movement, which occurs when the cap is Yengaged and upon continued advancement of the spindle, to swing the spinning members radially inward into enbers or, if desired, the two portions 41,42 may havea spline connection.

For the purpose of biasing the two portions of the frame into extended relation, a vplurality of .biasing springs 50 are provided,-preferably three in number, and spaced at equal intervals, Eachspring 50 is secured in place by a pin 51 at its upper end anda machine screw 52 at lower end. For the purpose of .limiting degree of extension of the portions of the frame,

the upper portion 41 includes `a screw 55, Athe head of which is received in a slot 56 formed in the mating portion. The springs 50-are preferably prestressedso that no relative telescoping movement occurs until an appre- -ciable axial force is exerted by the friction member 21 upon the cap thus insuring that the cap is twisted tight before it is locked in place. Means forachieving a predetermined twisting torque will be discussed at a later point.

For the purpose of converting the telescopingmovement of the frame to inward radial movement of-the spinning members, the spinning members are mounted upon arms which are pivoted toa lower portion 42 of the frame, with a cam and cam follower being provided at the upper end of each of the arms for camming the arms about their respective points of pivoting. Taking the spinning member 26 -by way of example, `it will be .noted that it is mounted upon an arm 61 which is cen- .trally pivoted at 62. At the upper end of the arm 61 a cam follower is providedin the form of a roller 63. To act upon the roller 63 a cam member 65 is provided which is in the form of a collar secured to the upper portion 41 of the frame. The fastening means consists of a plurality of screws 67 which are spaced at equal intervals and only one of which is visible-in FIG. l. The member 65, in addition to serving as a carn, also serves as a mount .for the pins 51 which retain the springs 50 and which have been previously referred to. The spinning members 26 are in the form of rollers which are retained on the respective arms 61 by circular nuts 68. Restoring force is provided by a garter spring 69 which may be in the form of an O ring of resilient material, suitable clips 50a serving to keep the garter spring away from the springs 5G.

It will be helpful at this time to consider a typical operating sequence of the parts thus far described. As the spindle 11is advanced downwardly while being simultaneously rotated, the chuck 20 engages a cap to which torque is frictionally applied by the friction member 21 within the chuck. Engagement between the chuck and the cap provides a reactive force so that, upon continued feeding movement of the spindle, the frame telescopes together against the force of the springs 50. During the telescoping movement the the cam member 65 is crowded against the cam followers 63 causing rocking of the arms 61 about the pivots 62 against the force of the garter spring 69 as shown in FIG. 3. `The spinning discs advance inwardly against the skirt 32 deforming the latter about the ridge 37 on the neck of the container. The spindle is then moved upwardly, restoring the two por- 4 tions of the frame to their extended position and withdrawing the cam member 65, thereby permitting the arms 61 to swing outwardly under the urging of the garter spring 69.

In accordance with one 0f the aspects of the present invention the device not only includes means for applyf ing frictional force to screw on the cap, but means are` further provided for limiting the amount of torque ap vplied to the cap to a precisely predetermined value. This is accomplished in the present instance by making the chuck 20 rotatable within the frame member 42 and by providing detent .means about the periphery of the chuck so that the chuck becomes stationary when the total detent force is exceeded. It will be noted in FIG. l that interposed between the chuck 20 and the member 42 is a ball bearing 70 of a type capable of resisting both axial loading and twisting forces. To provide detenting detent assemblies 71, 72, 73 are used, spaced at equal -intervals about the chuck and cooperating with notches.

74, 75, 76 formed in the chuck. Taking the detent assembly 71 by way of example it includes a detent plunger 81 having a head 82 and inwardly pressed by' means of a coil spring 83. A set screw 84 retains the: assembly and permits adjustment of the detenting force.. Corresponding parts are used in the detent assemblies. 72, 73. The tips of the detent plungers are preferably spherical in shape and the detent grooves 74-76 are pref-- erably straight-sided, having an included angle on the order of 90 degrees. It is found that the maximum torque may be predetermined with a high degree of accuracy and consistency using this arrangement. The coupling provides positive driving of the chuck 20 until a certain torque is achieved, a torque which will seal the cap to the neckbut which will, nevertheless, enable the cap to be removed by manual twisting. Following the achieving of this torque the detents leave the notches and clic idly about the chuck 20. During successive revolutions, and with the device operated at rated speed,. the detent plungers do not have time to seat in the notches at each revolution; consequently, there is no opportunity for the troque to achieve the value at which the initial release occurred, i.e., no hammering action.

For convenience in manufacture, the detent assemblies are received in a collar 85 which is closely fitted to the lower portion 42 of the frame and which is secured to the latter by means of machine screws 52, the collar 85 thus Ibecoming a more or less integral part of the member 42.

In accordance with one of the important aspects of the present invention, the frame 1S is mounted for limited locking movement, or articulation, with respect to the mount 12 so that when the capping head 10 is seated upon the cap of a container it is free to accommodate itself to the angling of the cap and the neck of the container to which the cap is aflixed; thus rotation of the frame proper takes place about the container axis or neck axis rather than about the axis of the driving spindle. Moreover, in accordance with the present invention guide surfaces are provided between the frame and the mount so that rocking of the frame occurs about a point centered on the chuck axis and lying slightly below the chuck, preferably at a level where the neck is fixed to the container and which may be conveniently referred to as the center of cocking. The above isl accomplished in the present construction by providing a guide assembly containing a first guide member or surface 91 which is fixed to the frame 15 and a second guide member 92 which is secured to the mount 12, with the members 91, 92 being in contact at an interface v'93. This interface is so formed as to provide ball-and socket action about a point 95 lying on the frame axis and spaced slightly below the level of the chuck as shown Yin FIG. 3. In accordance with one of the more detailed aspects of the invention, the interface 9-3 is not spherical as in the usual ball-and-socket connection but is conical,

lmade up'of mated cones having an angle of depression of about 14 degrees and with the guide members being biased toward one another to provide an automatic selfcentering action when the head is retracted from a container. Thus, in the present instance the upper guide member 92 is provided with a cylindrical upstanding sleeve 96 snugly telescoped within the mount 12 and which is downwardly biased by means of a coil spring 97. For the purpose of resisting the pressure of the spring 97 and to permit positive driving of the frame 15 even when the frame is rocked with respect to the drive spindle, the drive spindle is connected to the frame by means of a universal joint generally indicated at 100. This universal joint consists of a first pivoted block 101 at the lower end of the spindle 11 and a second pivoted block 102 at the upper frame member 41 joinedby a link 103, with the assembly being held together by pivot pins Y104; 105. The blocks 101, 102 are, moreover, pivoted on pins 106,* l-7 arranged at right angles to the pins 104, 105. It will be apparent, then, that the guide members 91, '92'permitl the frame to rock into accommodation with a cocked container neck with balland-socket action, butwhen the tool is retracted the conical surfaces, under the urging ofl spring 97, act to move into alinement with one another promptly thus restoring the frame to a centered condition with respect to the spindle in readiness to engage the next cap i in the series.

Since, as a `result of the construction, the chuck becomes precisely oriented with respect to the neck of the container, it follows that the spinning members, which are mounted in fixed position with respect to the chuck, also must assume precisely symmetrical positions with respect to the shoulder v37 formed on the neck of the container. Thus regardless of the angle of cocking of the neck on the container, each spinning member will be positioned as shown in FIG. 4, so that all of the spinning members will be effective to exactly the same degree in spinning the skirt of the cap against the shoulder 37 and with each spinning member applying constant spinning force against the metal during its entire 360 degrees of rotation. The result is to produce firm seating of the skirt portion of the cap against the shoulder 37 all of the way around with no clearance or crack between the cap and the shoulder inviting insertion of prying blade in an attempt to remove the same.

ln'accordance with one of the more detailed aspects of the invention, the mount 12 and the frame 15 are provided with anges having substantially the same diameter, and the mechanism is enclosed by means of a cylindrical enclosure formed of a flexible material having its upper and lower edges anchored to the respective flanges. Thus in the present embodiment the mount 12 is provided with a cylindrical flange 111 and the lower portion of the frame is provided with a flange 112 in general alinement therewith. Spanning the distance between the two flanges is a flexible enclosure member 113 of cylindrical shape held in place at its upper and lower edges by garter springs 114, 115 which may be in the form of O rings and which are seated in complementarily formed peripheral grooves. The enclosure serves to shield the assembly against the entry of `dirt or foreign objects, accommodates the rocking and telescoping movement referred to above, and gives the unit a more finished appearance.

While the operation of the device will be apparent from the above description it may be helpful to review it briey. rl`he spindle 11 is chucked for rotation and downward feeding movement into engagement with caps on a succession of containers which may be advanced in succession into a registered or alined position below the head. The means employed for coordinating the movement of the spindle and the transport of the containers is beyond the scope of the present invention and is a matter well understood by those skilled in the art. As the head is fed downwardly, the frame is in the alined i into contact with the friction member 21 within the chuck. When the cap is engaged it begins to turn, and, upon progressive advancement of the spindle, the cap is screwed down. As the spindle advances still further the chuck becomes firmly and fiatly seated upon the cap, and

the reaction pressure of the cap constrains the entire frame- 15 to rock about the point 95 with ball-and-socket action until the axis of the frame coincides with the neck axis of the container. Because Aof the at seating of vthe friction member (and. because Yof the bottoming of the capatthe end of its thread, the torque applied by the chuck rapidly builds upv until it exceeds the value forv which the detent assemblies have been set, following which the chuck becomes stationary and idle clicking occurs at the detent assemblies.

Y Upon still further advance ofthe capping head the cap offers sufficient reaction pressure so that relative telescoping movement takes placeV between the two portions 41, 42 of the frame accompanied by compression of the springs 50 which separate them. As a result of this relative movement, the cam member65 crowds downwardly against the cam followers y63 on the rocker arms 26-28 so that the spinning rollers move radially inward against the skirt portion of the cap, deforming such skirt portion about the shoulder 37 on the neck of the container as shown in detail in FIG. 4. In the present con-struction the sealing and spinning action takes place smoothly and without visible wobbling or vibration. the neck of `the container, unbalanced centrifugal `forces are minimized, and the head may be used at rotative and feeding speeds far beyond those of conventional heads. Consequently each spinning roller acts upon the cap with perfect symmetry.

After the spindle 11 reaches the lower end of its stroke, the spindle is retracted upwardly. During initial portion of the upward movement the isprings 50 act to separate the portions 41, 42 of the frame, retracting the cam 65 which permits the spinning members 26-28 to swing outwardly clear of the cap. This is followed by retraction of the chuck 20 away from the cap, whereupon the mating conical surfaces at the end of the frame are free, under the urging of the spring 97, to again come into alinement so that the head is in immediate readiness for its next downward stroke.

It will be apparent that the device not only overcomes the disadvantages of prior devices intended for this purpose but is simple to construct, capable of operating reliably, without maintenance, over long periods of time. Moreover, the device is radially compact enabling use closely adjacent handles or other obstructions.

While we prefer to use a friction member of rubber or the like for engaging the top of the cap since this provides smooth and progressive torque transmission, nevertheless it will be apparent that the invention is not limited thereto but includes the possibility of roughening the surface of the engaging member or providing irregularities thereon which mate with irregularities on the cap `itself to provide a more positive or keyed type of engagement, Consequently the term frictional shall be interpreted in the following claims in the broad sense of contact between surfaces which are pressed together and which are so surfaced or formed as to be capable of transmission of torque from the frame of the device to the cap.

We claim as our invention:

A l. In a capping machine for applying a tamper-proof cap to the threaded neck of a container having a shoulder formed thereon, the combination comprising a drive spindie, a mount atthe lower end thereof, a frame in engagement with said mount, a chuck on said frame having means for frictionally vengaging the upper end of the cap to screw the same into seated position on the neck of the Sincethe frame is alinedV withV container, spinning means on said frame for engaging the skirt portion of the cap for spinning the same about said shoulder when the cap is in seated position, guide surfaces between said frame and said mount for enabling limited ball-and-socket rocking movement of the frame about a point located adjacent said chuck and on the axis of the latter so that the chuck and frame as well as the spinning means on the latter are free to aline themselves with the seated cap on the container, and a drive connection interposed between the spindle and the frame for insuring positivedriving movement therebetween in all positions of the frame. Y

2. In a capping machine for applying a tamper-proof cap to the threaded neck of a container having a shoulder formed thereon, the combination comprising a drive spindle,1a mount at lthe lower end thereof, -a frame on said mount, a chuck on said frame having means for frictionally'engaging. the upperrend o f the cap to screw the latter into seated position on the v container, spinning 4means on said frame for engaging the skirt lportion of the cap,` means for actuating the-spinning means after the cap has been substantialy Yscrewed'int'o seated position; means permitting limited articulation between'the mount and said frame so that said frame may accommodate itself to a container having a neck in cocked position, said chuck being lbodily rotatable in said frame and having a detent connection therewith so that the chuck is free to rotate after aV predetermined torque is-achieved.

3. In a cappingv machine for applying a tamper-proof cap to the threaded neck of a container having a shoulder formed thereon, the combination comprising a spindle, a mount at -the lower end thereof, a frame on said mount, a chuck rotatably `mounted on said frame and having means for frictionally engaging the upper end of the cap to screw the ylatter into seated position on the containena clutch interposed between `the chuck `and the frame so adjusted and arranged that the chuck applies a predetermined amount of torque to the cap, spinning means on said frame for engaging the skirt portion of the cap, said frame being mounted for limited axial movement and having springs for resiliently supporting the same on said vmount for relative movement in response to reaction pressure as the chuck is brought into full engagement with the cap, and meansresponsive to said relative movement for actuating the spinning means, said springs being sufficiently strong so that slippage occurs at said clutch prior to full actuation of said spinning means.

4. In a capping machine for applying a tamper-proof cap to the threaded neck of a container having a shoulder formed thereon, the combination comprising a drive spindle, a mount at the lower end thereof, a frame in engagement with said mount, a chuck on said frame having means for frictionally engaging the upper end of the cap to screw the same into seated position on the neck of the container, spinning means on said frame for engaging the skirt portion of the cap for spinning the same about said -shoulder when the cap is in seated position, guide surfaces between said frame and said mount for enabling limited ball-and-socket rocking movement of the frame about a point located adjacent said chuck and on the axis of the latter so that the frame and chuck are free to assume a position of alinement with the cap, the guide surfaces on the frame and mount being in the form of mated cones, and means for biasing the surfaces together so that when the spindle is retracted the frame is returned automatically into a position of alinement with the spindle in readiness for acting upon a successive container.

5. In a capping machinefor applying a tamper-proof cap to the threaded neck of a container having a shoulder formed thereon, the combination comprising a drive spindle, a mount at the lower end thereof, a frame in engagement with said mount, a chuck on said frame having means for frictionally engaging the upper end of the cap to screw the sameinto seated position on the neck of the container, spinning means on said frame for engaging the skirt portion of the cap for spinning the same about said'. shoulder when the cap is in seated position, means providing limited ball-and-socket rocking movement of the frame with respect to the mount, the center of the balland-socket movement being spaced slightly below saidl chuck and substantially coinciding with the region of attachment of the neck to the container to permit movement of the chuck and frame and the attached spinning means into alinement with the cap, and means for restoring the frame to a center position when the spindle is retracted.

6. In a capping machine for applying -a tamper-proof cap to the threaded neck of a container having a shoulder formed thereon, 4the combination comprising a drive spindle, a mount at the lower end thereof, a frame in engagement with said mount, a chuck on said frame having means for frictionally engaging the upper end of the Vcap to screw the same into seated sealing position on the neck of the container, spinning means on said frame for engaging the lower skirt portion of the cap for spinning the same about said shoulder when the cap is in its seated position, a. pair of mated conical members interposed between said frame and said mount for enabling limited rocking movement of the frame so that the chuck and frame as well as the spinning means on the latter are free to assume a position of alinement with the cap when the spindle is lowered bringing the chuck into forceable engagement with the cap, and means for restoring the frame together with the chuck and spinning means thereon into alinement with the spindle when the chuck is retracted from the cap.

7. In a capping mechanism for applying a tamperproof cap to the threaded neck of a container having a shoulder vformed thereon, the combination comprising a drive spindle, a mount at the lower end of the drive spindle, a frame secured to the mount and having provision for limiting rocking movement with respect to the latter, a chuck at the lower end of the frame for frictionally engaging the top of the cap, said frame having upper and lower portions telescoped together with means for biasing the lower portion relatively outward, spinning means on the lower portion of the frame for engaging the skirt portion of the cap, means for actuating the spinning means after the chuck is seated on the cap and upon relative telescoping between the portions of the frame incident to continued advancement of the spindle, tht mount and the lower portion of the frame each having flanges of substantially the same diameter and spaced from one another, and a cylindrical enclosure of exible material having substantially the same diameter as the flanges and secured to the anges along its respective upper and lower edges to enclose the mechanism while permitting the relative rocking movement between the frame and the mount.

8. In a capping machine for applying a tamper-proof cap to the threaded neck of a container having a shoulder formed thereon, the combination comprising a drive spindle, a mount at the lower end thereof, a frame having first 4and second telescoping portions keyed together at the lower end of said mount, means for biasing the rst portion of the frame downwardly with respect to the second portion into a predetermined extended position, a chuck on said frame having means for frictionally engaging the upper end of the cap to screw the same into seated position on the neck of the container, spinning means on said frame for engaging the skirt portion of the cap for spinning the same about said Shoulder when the cap is in seated position, guide surfaces between said frame and said mount for enabling limited ball-and-socket rocking movement of the fr-ame about a point located adjacent said chuck and on the axis of the latter so that the chuck and frame as well as ythe spinning means on the latter are free to aline themselves with the seated cap on the container, anda drive connection interposed between the spindle and the frame for insuring positive driving move- 10 ment therebetween n all positions ofthe frame, said spin- References Cited in the file of this patent ning means including a cam and cam follower associated with the first and second portions of the frame as the UNITED STATES I )ATENTS two portions of the frame telescope together upon progres- 2'42275 Rue, June 24: 1947 sive advancement of the spindle and in response to re- 5 2,672,269 Resma Mar- 161 1954 Y action forces from Said cap. Ranney et aL Jan- 17; 

1. IN A CAPPING MACHINE FOR APPLYING A TAMPER-PROOF CAP TO THE THREADED NECK OF A CONTAINER HAVING A SHOULDER FORMED THEREON, THE COMBINATION COMPRISING A DRIVE SPINDLE, A MOUNT AT THE LOWER END THEREOF, A FRAME IN ENGAGEMENT WITH SAID MOUNT, A CHUCK ON SAID FRAME HAVING MEANS FOR FRICTIONALLY ENGAGING THE UPPER END OF THE CAP TO SCREW THE SAME INTO SEATED POSITION ON THE NECK OF THE CONTAINER, SPINNING MEANS ON SAID FRAME FOR ENGAGING THE SKIRT PORTION OF THE CAP FOR SPINNING THE SAME ABOUT SAID SHOULDER WHEN THE CAP IS IN SEATED POSITION, GUIDE SURFACES BETWEEN SAID FRAME AND SAID MOUNT FOR ENABLING LIMITED BALL-AND-SOCKET ROCKING MOVEMENT OF THE FRAME ABOUT A POINT LOCATED ADJACENT SAID CHUCK AND ON THE AXIS OF THE LATTER SO THAT THE CHUCK AND FRAME AS WELL AS THE SPINNING MEANS ON THE LATTER ARE FREE TO ALINE THEMSELVES WITH THE SEATED CAP ON THE CONTAINER, AND A DRIVE CONNECTION INTERPOSED BETWEEN THE SPINDLE AND THE FRAME FOR INSURING POSITIVE DRIVING MOVEMENT THEREBETWEEN IN ALL POSITIONS OF THE FRAME. 